Animal feed represents one of the largest costs incurred in keeping livestock and other animals. The use of various enzymes in animal, e.g. livestock, feed has become almost common practice. These enzymes are usually produced by culturing micro-organisms in large scale fermenters operated by industrial enzyme producers. At the end of the fermentation the resulting “broth” is usually subjected to a series of filtration steps to separate the biomass (the micro-organisms) from the desired enzyme (in solution). Subsequently the enzyme solution is concentrated and processed as a liquid (often after addition of various stabilisers) or to a dry formulation.
Liquid and dry enzyme formulations are used on a commercial scale by the feed industry. Liquid enzyme formulations may be added to the feed after pelleting in order to avoid heat inactivation of the enzyme which would occur during the pelleting process. However, the amounts of enzyme in the final feed preparations are usually very small which makes it difficult to achieve a homogeneous distribution of the enzyme in the feed, and liquids are notoriously more difficult to mix evenly into the feed than dry ingredients. In addition one needs specialised (expensive) equipment to add liquids to the feed after pelleting which is not currently available at most feed mills (due to the extra cost).
Dry enzyme formulations may be added to the feed before pelleting and therefore are subjected to heat-inactivation during pelleting. Preferred manufacturing protocols in the feed industry involve steam pelleting where the feed is subjected to steam injection(s) prior to pelleting, a process called conditioning. In the subsequent pelleting step the feed is forced through a die and the resulting strands are cut into suitable pellets of variable length. The moisture content immediately before pelleting is generally between 13% and 16%. During this conditioning process temperature may rise to 60–95° C. The combined effect of high moisture content and high temperature is detrimental to most enzymes. These disadvantages are also encountered in other types of thermomechanical treatments such as extrusion and expansion.
In order to overcome these problems, EP-A-0,257,996 suggests that the stability of enzymes in feed processing could be increased by the preparation of an enzyme “premix” where an enzyme-containing solution is absorbed onto a grain-based carrier consisting of flour, and the premix is subsequently pelleted and dried. However, these flour-based premixes are not suitable for more gentle methods of processing (of the dough-like premix) into granulates, such as low-pressure extrusion or high shear granulation, because of the gluey character of the flour-based premixes.
Various enzyme manufacturers have developed alternative formulation methods to improve the stability of dry enzyme products during pelleting and storage.
EP-A-0,569,468 refers to a formulation consisting of an enzyme-containing granulate that is coated with a high melting wax or fat alleged to improve resistance to pelleting conditions. The granulate is prepared by mixing a dry inorganic (e.g. sodium sulphate) carrier with the enzyme solution in a high shear granulator. As a consequence of the fat coating, the dissolution time of the granulate is long (about one hour). Therefore, the bioavaibility of the enzyme to the animal is decreased. In addition, the granulates have a wide particle size distribution. This makes it difficult to obtain an evenly distributed enzyme concentration after coating, since small particles absorb a relatively high amount of coating agent as compared to large particles. EP-A,569,468 further teaches that any beneficial effect of the coating with respect to pelleting stability is specific for the type of granulate coated, which in this case is based on a sodium sulphate carrier. However, the absorption capacity of these (sodium sulphate) carriers is much less than that of carriers such as flour, which is undesirable if one wishes to produce more concentrated enzyme-containing granulates.
WO97/39116 discloses formulations consisting of a preformed granule which is capable of absorbing at least 5% water. However, with these formulations a satisfactory solubility rate can only be achieved with very powerful mixing. Such formulation may therefore be effective in the detergent area but not in the intestinal tract of the animal.
WO98/54980 discloses enzy containing granules containing edible carbohydrates, of which preferably starch. Although these formulations readily dissolve in water and thus ensure a good bioavailability, the pelleting stability of these starch-based granulates is less than those obtained with the fat-coated granulates described above.
WO98/55599 demonstrates that high concentration phytase compositions which are cheaper to produce show an increase in stability, especially during a pelleting process in the preparation of animal feed (pellets). However, the pelleting stability of these compositions is also still beyond the stability obtained with the fat-coated granulates described above.
There is thus still a need for stable formulations of enzymes for use in animal feed that are cheap to produce, that combine a satisfactory pelleting stability with good bioavailability of the enzyme to the animal, and that have an optimal storage stability.